Tissue expansion is a known technique involving not merely the stretching of skin but the production of new skin. The process involves the use of the well known fact that skin, when placed under significant tension, will not only stretch but generate new skin which can be used for covering open wounds and other skin defects. In the treatment of baldness, particularly in the mid scalp and crown regions, the prior art teachings deemed most relevant involve the use of implantable tissue expander bags or balloons. These devices are implanted under hair-bearing portions of the scalp and are inflated with a liquid to expand an area of the scalp bearing relatively dense hair while not stretching an area of bald or sparse hair. A stretched flap of the skin bearing the relatively dense hair is then transposed and grafted to the area lacking hair after removal of a corresponding portion of the skin in the non-hair bearing region. A more detailed description of these techniques is found in the work Aesthetic and Reconstructive Surgery of the Scalp by Toby G. Mayer and Richard W. Fleming, Mosby Year Book, Inc., especially Chapters 12 and 14.
A related technique for tissue expansion which is described as useful in the preoperative expansion of skin tissue and also in the treatment of baldness is found in Cohen and Cosmetto, J. Dermatol. Surg. Oncol. 1992; 18:112-123. The devices utilized in the Cohen et al article are further described in U.S. Pat. No. 5,127,412, issued Jul. 7, 1992. The devices described in U.S. Pat. No. 5,127,412 comprise an anchor member positioned at one side of an incision and a ratcheting winder which draws a single loop of suture material across the incision, thus stretching the skin and/or closing a wound.
Although the techniques and equipment described just above are useful for the replacement of non-hair bearing scalp with hair-bearing scalp, problems exist which have hampered more wide spread acceptance. One problem with the balloon-type tissue expanders stems from the length of time that the devices must remain in place to complete the process. For the patient, this raises what is primarily a cosmetic problem. The time required may be as much as six to eight weeks, and especially during the later weeks, the effects of the tissue expansion process are difficult to conceal. The appearance of large, somewhat grotesque protuberances on the scalp, or even external tensioning devices, is impractical to disguise and, as a consequence, is something that many potential patients are unwilling to accept, especially since few people can avoid appearing in public for very long periods of time. In addition, during the period of tissue expansion, which averages about eight weeks, bi-weekly visits to the physician's office are necessary to complete the inflation process.